[SOLVED]820-2850 no backlight

MDY

New member
This laptop was working ok, video and backlight.
I opened this laptop to replace a cap and now when I tested, has video (can see blinking folder) but no backlight. I checked led driver LP8545 and has a hole. I replaced it with new one and check for short before and after the diode. No short. After replacment I do have 25 at PPVOUT_S0_LCDBKLT. I check this on diode and on lvds connector, but still no backlight, only blinking folder.
I tested with another working screen and lcd cable and no backlight. What is next to check?
 

dukefawks

Administrator
That is all fine and 25V would also mean there should be backlight. Check on diode mode if pins 38-40 actually have continuity to the other end of an LCD cable.
 

MDY

New member
I dont have opened screen to check but I tested with another screen and LCD cable assembled and no backlight. Replace LVDS connector is worth it?
 

MDY

New member
I just took a lcd cable I have for 2012 model and put it on this board and I tested 3 backlight pins and all them goes to the other end of LCD cable. In the other end I found 2 pines. Pin2 and pin3.
 

MDY

New member
I did pram and smc reset. Still no backlight, but PWM goes higher yes.

PWM - 2.45V
BKLT_EN - 3.1V
After D9701 - 24.82V
 

MDY

New member
With lcd and screen conected pins

31-36 0.671/0L

Red to ground - 0.671
Black to ground - 0L
 

MDY

New member
I did what you told me. Now in pin2 of LP8545 I have 3.28V, and after D9701 I still have the same 24.82V. Still no backlight. Obviously it is not PWM problem. What more can could be?
 

MDY

New member
I took again another macbook 2010 and put there the motherboard and I affirm the same. I have video, I see the folder blinking but missing backlight with another screen and LCD cable.
It is board issue, but what more could be?
 

dukefawks

Administrator
I have no idea. Compare the 25V to another 15" machine. It could be bad solder or dead LP8545 again. Check resistors around the LP8545 and check if no components were moved/blown off while replacing LP8545.
 

MDY

New member
But need to understand what screen expect from board to turn on LEDs? Which signals? In laptops expect 12-19V, PWM and enable. And in apple?
 

dukefawks

Administrator
25V is not that low but it could be higher.
On a working 2010 15" BKL output is 33V and LED return lines are 3.2V so that puts about 30V across the LEDs
 

MDY

New member
And how do you think these LED driver got burn? This is second macbook pro for 2 weeks. One is 2010 15, and another 2012 15
Both of them working good, video, backlight. I just opened them to replace a cap and after that backlight is gone. In both cases I found hole in LP8545
I dont know what wrong I do...why this led driver just got damage. In first case board 2012 I just replaced it and it works good.
 
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